Talk about something you both share an interest in. If you don't share any interest than
a) she shouldn't be your crush or
b) do your research before hand and find something you are both interested in.

I've always found that the easiest way to approach a girl, is to find a common interest and start talking about it.

This could be something as simple as having the same type of phone, her clothes that's touchy, be careful , her job (people really like talking about work, especially when they're not talking to a co-worker), her ringtone I had a girl had her phone go off in class. It was the "hey, listen!" navi says in LoZ OoT. That immediately sparked a conversation., or in uncommon cases, video games, internet websites, and anime.

You calm down and act natural.
By which I mean just act like what you'd act like with everyone else, before you do something ask yourself "Would I do this with everyone else?" if the answer is no then don't do it.

Jeez you guys aren't in a relationship, they're just your crush. So just play it cool.

I'm going to go bald like at 34 judging by how things are going and what happened to my dad. If I'm not dead by now I'll just get transplants. Just pray you keep it long enough to get money to do the same.